Insulating-support.



C-LE G.FORTESCUEn INSULATING SUPPORT.

APF'iCATlON FILED MAY 25. I914.

INVENTOR [bar/e5 [a 6 firfesc 06 ATTORNEY UNITED STATES PATENT ormon.

flsIdIARLElS LE G. FOREEESCUE, OF FITTSBURGH, PENNSYLVANIA, ASSIGNOR T WESIIHG- IHCIU ELEfilllEjtliC AND MANUFZWITUREIQ'G EGMPANY, A CQBPORATIEQN 0F :PENN- ain, a resident of county of Allegheny and State of Pennylmay be represented by means celain insulators having corr sunvnnin.

INSULAEIEG'SUPPGET.

Application filed may 25, 191%.

To all whom it may concern Be it known that 1, CHARLES Ln fruscm, a SLllJjQCl) of the King of Great Brit- Fittsburgh, in the vania, have invented a new and useful improvement in Insulating-Supports, of which the following is a specification.

My invention relates to insulators, and it has particular reference to insulating supports adapted to insulate high-potential lines or conductors.

When a difference of potential exists between adjacent conducting bodies, the air or other interposed insulating medium is subjected to stresses, by reason of the electric field produced. A field of this character of the lines called electrostatic flow lines, the distribution and arrangement of which are dependout upon the shapes and sizes-of the conducting bodies, their spacing, the character and shape of the insulating medium, and the potential of the bodies.

Heretofore insulating bod;

such as por- (1 surfaces or otherwise so constructed as to provide very long surface distances, have seen interposed between conducting bodies in order to insulate them from each other. It was intended that these insulating bodies, by providing long leakage paths between the conducting bodies, would substantially preclude the occurrence of surface discharges.

It is well known that discharges of this kind occur when the air adjacent to the insulating bodies is subjected to undue concentrations of potential stresses which may result from the incorrect shapes of conducting terminals, or from the incorrect form of insulating bodies, or from both of said factors.

As disclosed in patent application of Bandall, Farnsworth and Fortescue, Serial No. 558,74A, filed April 30, 1910, and assigned to Westinghouse Electric 85 Manufacturing 'Gompany, the concentration of potential stresses attributed to the incorrect form of insulating bodies may be entirely avoided by making their shapes such as to conform to the electrostatic lines of force which would represent the existing electric fields between the'conducting bodies if they were located in a homogeneous insulating medium, such as air.

Specification of Letters Patent.

r l Again, the concentration of potential Patented Mara-12, 1918.

Serial 230. 846,791.

stresses attributed to the incorrect shape of the conducting terminals may be substantially precluded by modifying the form of their adjacent and opposed surfaces.

lllorecver, the insulating strength of a transm1ssion line support may be increased if the external electrostatic field surrounding the support is so distributed as to insure the distribution of uniform surface stresses thereupon, as disclosed in my patent application, Serial No. 837,742, filed May 11, 191

One object of my invention is to provide an insulating support for high-voltage conductors which is adapted to utilize, to substantially its full insulating value, the air or other insulating medium in which the convide an insulating support that, for a given voltage, will be of smaller dimensions than those heretofore utilized for a similar voltage, or that, for a given size, may be capable of withstanding higher voltages than insulators not built in accordance with my invention.

In the accompanying drawing, Figures 1 and 2 are, respectively, a sectional and a plan View of an insulating support embodying a form of my invention. Fig. 3 is, a sectional View of oneof my insulating elements. Fig. 4c is a sectional view of a modification of the insulator shown in Fig. 1.

Referring to Figs. 1 and 2, a high-potential conductor 1 is secured, by means of'a clamping device 2, to an insulating support. 3 which is secured to a memberd by means of a pin 5. The support 3 comprises a se 'ries of elements or condensers 6 superposed upon one another, as shown. An upper element 7 is provided with an electrode 8 which extends laterally beyond the intermediate elements 6. The edge 9 of alower element engages the support f which is made of conducting-material and of such extent as to present a surface to the adjacent and opposite surface of the upper electrode 8.

As shown in Fig. 3, eaiIh of the elements 6 comprises a metal hell or petticoat llginto which is molded an insulating compound 12. A recess 13 is provided in order that the adjacent bell may be nested therein, as shown in Figs. 1 and l. The exposed surface 14 of the dielectric or insulating cornpound 12, which is intercepted between two adjacen t'bells, is so molded as to conform to the lines of the electric field between two adjacent bells. As above explained, this configuration of the exposed surface of the ties of my insulator, it is highly desirable to obtain equal divisions of potential difference between the insulating elements or condensers 6, but this is not the only condition for a successful design. The aforementioned condition may actually be obtained, and yet the system of elements will break down at a very much lower potential difference than the sum of the break-down strengths of each element. To increase the strength of my insulator, the external electrostatic field surrounding the same should be so distributed as to insure a substantially uniform surface distribution of the electrostatic stresses imposed thereupon. For this purpose, I have provided the electrode 8 and the conducting member 4.

-When it is preferred to have the most ,efii- Y 'cient design of my insulator and to minimize its overall length, it is desirable for .maximum efficiency that the external electrostatic field be substantially uniform and agree with the division of potential between the individual elements 6 comprising the structure 3. The electrodes 8 and 4: are supplied to approximate the result which would be obtained by bounding the insulating support 3 by infinite parallel conducting planes perpendicular to the axis of the insulator.

As above mentioned, this will effect a substantially uniform distribution of the electrostatic field external to, and surrounding, the insulator 3. The condition for equal division of potential between the element 6 is that the flux leaving each metallic bell 11 shall be of the same quantity; this means that the capacity of each bell 11 to ground must be inversely as its potential, and that the capacity between adjacent pairs of bells must be equal. This is approximated very closely if the bell of the upper or high- 1 potential element 7, and the bell of the lower or ground potential element 10, coincide at their edges with the electrodes 8 and 4, respectively. An insulator made according to the above plan conforms to the law of uniform fields and is insured against concentrations of electrostatic stresses upon its surfaces. Again, if the dimensions of the insulating structure are double, the capacity of the insulator to resist high potentials is substantially doubled.

It is unnecessary, to obtain good results, however, to so design the insulator as to effect an equal division of the potential difference between the various elements comprising the support. If each of the elements 6 assumes its proper share of the potential difference between the conductor 1 and the support 4, and asubstantially uniform distribution of the electrostatic field surrounding the support. 3 is obtained, the support has a very high insulating value. Of course, with this approximation, the maximum efliciency is not obtained.

Referring to Fig. 4, an insulator is shown which is very similar in construction to that shown in Fig. 1. The elements '6 are superposed upon one another, the upper element 7 being provided with an electrode 15, and the lower element 10 being provided with an electrode 16. The insulator may be secured to any tower or pole by engaging a pin (not shown) which may project into the element 10 or by "securing the electrode 16 upon a properplatform. In this modification, an equal division of potential between the elements 6 may be easily effected because the lower edge of the higlrpotential electrode 7 and the lower edge of the low-potential electrode 1O coincide or lie in the same potentialplanes as the parallel and laterally-extending or flux-distributing surfaces of the discoidal shaped bodies or electrodes 15 and 16, respectively. What is said relatii e to the insulator of Fig. 1 in regard to the maximum efiiciency to be obtained therefrom may be said with equal effectiveness respecting the insulator shown in Fig. at.

Although I have shown and described devices of specific structural details, many modifications may be effected therein within the spirit and scope of my invention, and I desire that only such limitations shall be imposed as are indicated in the appended claims- I claim as my invention:

1. An insulating structure comprising a plurality of superposed substantially bellnested within one another, extensions for the upper and lower members that extend laterally beyond the said members, and bodies of insulating material interposedbetween adjacent conducting members, the exposed surmg members so disposed that their edges coincide with the edges'of the said upper and lower conducting members.

a. An insulating structure comprising aplurality of superposed, equally spaced and nested bell-shaped conducting members, bodies of insulating material interposed between adjacent conducting members which extend laterally beyond the insulating bodies, and laterally extending electrodes for the upper and lower conducting members so disposed that their lower edges coincide with the edges ofthe said upper and lower conducting members.

5. An insulating structure comprising a plurality of similar bell-shaped conducting members which are superposed, equally spaced from andnested within one another, bodies of insulating material interposed between adjacent conducting members which extend laterally beyond the insulating bodies, and discoidal shaped extensions of conducting material for the upper and lower conducting members so disposed that their edges coincide with the edges of said upper and lower conducting members in order to obtain the substantially equal division of potential difference between the conducting members.

6. An insulating structure comprising a plurality of superposed substantially bellshaped conducting members which are nested within one another, bodies of insulating material interposed between adjacent conducting members, the exposed surfaces of the insulating bodies being shaped to substantially conform to the direction of the lines of force oi' the electric field existing between the adjacent conducting members, said conducting members extending laterally beyond the insulating bodies, and extensions for the upper and lower members that ex.- tend laterally beyond the said members, and that are disposed to have their edges coincide with the edges of the said upper and lower conducting members in order to obtain a substantially equal division of the potential differences between the said bellshaped members.

7. An insulator comprising a built-up column of hollow conical-shaped conducting members of equal size, and interposed conical-shaped bodies of insulating material that are severally provided with conical indentations, said insulating bodies being received in the upper conducting members and the lower conducting members being received in the conical indentations of the insulating bodies.

In testimony whereof, I have hereunto subscribed my name this 21st day of May, 1914.

CHARLES LE G. FORTESCUE. lNitnesses:

GoLnm E. MoGEE,

B. B. HINEs. 

